Late last week, I took a look back at polls since Rick Perry entered the race and noticed that the combined support of the four Not Romneys—Michele Bachmann, Herman Cain, Newt Gingrich, and Rick Perry—has been surprisingly stable, even though the there's been huge ups and down for the individual candidates.
I then looked at hypothetical head-to-head matchups between Mitt Romney and whoever his chief "Not Romney" rival happened to be at the time of the poll (in August and September it was Perry, October it was Cain, and November it was Gingrich). The results told the same story
Both of these charts show that there are consistently more Republicans eager to nominate a Not Romney than to nominate Mitt Romney. Obviously, that's not good news for Romney, but because Republicans have failed to coalesce behind a single alternative, Romney has consistently been one of the top two candidates in national polling, seemingly validating his divide-and-conquer strategy.
The problem with his plan, however, is that it falls apart if Not Romney supporters begin to coalesce around a single candidate. Yesterday's endorsement of Newt Gingrich by the New Hampshire Union Leader suggests that is exactly what's happening.
According to Nate Silver's research, the candidate who gets the Union Leader's endorsement tends to rise by about 11 points in the polls after getting the endorsement. One of Nate's key points is that this isn't necessarily a cause-and-effect thing: it could be the endorsement merely reflects a broader trend—that it's a "leading indicator" as Nate puts it. And if the endorsement reflects a move by the Republican base to coalesce around Newt Gingrich, then Mitt Romney is in a ton of trouble. His path to the nomination depends on the weakness of his opposition. He cannot win against tough rivals. And if he can't beat Newt Gingrich or the rest of the field, then he can't even beat weak rivals.